Short-sequence ecf bleaching process x/z/d-eop-d or x/d/z-eop-d for kraft wood pulp

ABSTRACT

The present disclosure belongs to the technical field of papermaking, and specifically relates to a short-sequence ECF bleaching process X/Z/D-E OP -D or X/D/Z-E OP -D for kraft wood pulp, comprising the following steps: (1) sequential bleaching (X/Z/D or X/D/Z): subjecting an oxygen delignified wood pulp to X/Z/D 1  or X/D 1 /Z sequential bleaching to prepare a semi-bleached pulp; (2) reinforced alkaline extraction treatment (E OP ): performing hydrogen peroxide and oxygen enhanced alkaline extraction treatment on the pulp after sequential bleaching to further dissolve the residual lignin in the pulp; (3) supplemental bleaching (D): performing a chlorine dioxide supplemental bleaching on the pulp after the enhanced alkaline extraction treatment to obtain a fully bleached pulp (88% ISO).

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims the benefit and priority of Chinese Patent Application No. 202010788729.5 filed on Aug. 7, 2020, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.

TECHNICAL FIELD

The present disclosure belongs to the technical field of papermaking, and specifically relates to a short-sequence ECF bleaching process X/Z/D-E_(OP)-D or X/D/Z-E_(OP)-D for kraft wood pulp.

BACKGROUND ART

The statements herein only provide background information related to the present disclosure, and do not necessarily constitute prior art.

The level of production and consumption of paper and cardboard has become an important indicator of the economic development and social progress of a country. Although China has become the world's largest producer and consumer of paper products, the paper industry is facing the problem of shortage of fiber resources and a large burden of environmental pollution. Therefore, low-carbon economy and green technology have become the themes of the development of the paper industry. Exploring clean bleaching technology with low energy consumption and low pollution has always been a research hotspot of scientific and technological workers.

In order to meet the requirements of the recycling, low-carbon, and green economy development model, and solve the problems of high pulp production cost, poor paper quality and environmental pollution during the current pulping and bleaching process, many papermaking companies have gradually abandoned traditional pulping and papermaking technology, and adopt cleaner and environmentally friendly pulping bleaching technologies, such as elemental chlorine-free bleaching (ECF), total chlorine-free bleaching (TCF) and biological bleaching technologies. ECF bleaching technology uses ClO₂ instead of traditional chlorine and hypochlorite, which significantly reduces environmental pollution, but the chlorine element in ClO₂ bleaching agent is still harmful to the environment.

SUMMARY

In order to improve and solve the technical defects and shortcomings of the existing bleaching technology, the present disclosure provides an elemental chlorine-free bleaching process for fast-growing eucalyptus pulp, i.e., an ozone-containing elemental chlorine-free bleaching process (Z-ECF), which is used to prepare high-brightness kraft pulp, under the premise of ensuring the physical strength of the kraft bleached pulp into paper, the amount of ClO₂ bleaching agent and the water consumption of pulp washing in the bleaching process are reduced.

The present disclosure is realized through the following technical schemes: the concentration of the pulp involved in the following is mass percentage unless otherwise specified; the dosage of reagents and chemicals involved, unless otherwise specified, are relative to the absolute dry pulp.

According to the first aspect of the present disclosure, a short-sequence ECF bleaching process for kraft wood pulp is provided, wherein it comprises the following steps:

-   -   Subjecting an oxygen delignified wood pulp to X/Z/D₁ or X/D₁/Z         sequential bleaching to prepare a semi-bleached pulp;     -   Performing hydrogen peroxide and oxygen reinforced alkaline         extraction treatment on the pulp after sequential bleaching;     -   Performing a chlorine dioxide supplemental bleaching D₂ on the         pulp after the reinforced alkaline extraction treatment to         obtain a fully bleached pulp;

Wherein, in the X/Z/D₁ or X/D₁/Z sequential bleaching, no pulp washing is between X, Z, and D₁ bleaching.

The present disclosure adopts X/Z/D-E_(OP)-D or X/D/Z-E_(OP)-D bleaching treatment to obtain pulps with higher brightness and strength performance indexes.

Compared with the traditional D-E_(O)-D-D bleaching process, the X/Z/D-E_(OP)-D orX/D/Z-E_(OP)-D bleaching sequence reduces a chlorine dioxide bleaching stage. At the same brightness of the final pulp, the chlorine dioxide consumption is reduced by more than 30%, and the water consumption is reduced by more than 20%.

According to the second aspect of the present disclosure, a fully bleached pulp prepared by the process described in above technical scheme is provided.

The high-brightness kraft pulp prepared by the above ozone-containing elemental chlorine-free bleaching (Z-ECF) of the present disclosure can reduce the amount of ClO₂ bleaching agent in the bleaching process while ensuring the physical strength of the kraft bleached pulp into paper and the water consumption of pulp washing.

According to the third aspect of the present disclosure, application of the above fully bleached pulp in the production of paper and cardboard is provided.

Because the present disclosure can reduce the amount of ClO₂ bleaching agent and the water consumption of pulp washing in the bleaching process under the premise of ensuring the physical strength performance of the kraft bleached pulp into paper, it is expected to be widely used in the papermaking industry.

The beneficial effects of the present disclosure are as follows:

-   -   (1) The present disclosure adopts X/Z/D-E_(OP)-D or         X/D/Z-E_(OP)-D bleaching sequence treatment to obtain pulp with         higher brightness and strength performance indexes. Compared         with the traditional D-E_(O)-D-D bleaching sequence, the         X/Z/D-E_(OP)-D or X/D/Z-E_(OP)-D bleaching sequence reduces a         chlorine dioxide bleaching stage, at the same brightness of the         final pulp, the amount of chlorine dioxide is reduced by more         than 30%, and the water consumption is reduced by more than 20%.     -   (2) The method of the present disclosure is simple, low in cost,         strong in practicability, and easy to popularize.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It should be noted that the following detailed descriptions are all exemplary and are intended to provide further descriptions of the present disclosure. Unless otherwise specified, all technical and scientific terms used in the present disclosure have the same meanings as commonly understood by those of ordinary skill in the technical field to which the present disclosure belongs.

It should be noted that the terms used here are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms “comprising” and/or “including” are used in this specification, they indicate that there are features, steps, operations, devices, components, and/or combinations thereof.

A short-sequence ECF bleaching process X/Z/D-E_(OP)-D or X/D/Z-E_(OP)-D for kraft wood pulp, comprising the following steps:

-   -   (1) Pulp preparation: subjecting the wood chips after cooked by         kraft pulping to washing and screening to obtain a natural pulp;         then subjecting the natural pulp to oxygen delignification or         enhanced oxygen delignification to prepare the pulp.     -   (2) ECF bleaching: subjecting the above pulp to X/Z/D₁-E_(OP)-D₂         bleaching, where X/Z/D₁ stage or X/D₁/Z stage is sequential         bleaching, no pulp washing is between X, Z and D bleaching, and         pulp washing is performed between X/Z/D₁ stage or X/D₁/Z stage         and E_(OP) stage and D₂ stage.

The bleaching process conditions: X/Z/D₁ or X/D₁/Z stage: xylanase-assisted bleaching (X), the conditions are as follows: the amount of xylanase is 5-20 U/g pulp, the pulp concentration is 10-15%, pH=5-9, the bleaching temperature is 50-80° C., and the bleaching time is 60-120 min; After bleaching, the pulp is not washed, and directly subjected to ozone bleaching (Z), the conditions are as follows: the bleaching temperature is 50-80° C., the pulp concentration is 10-15%, pH=2-4, the bleaching time is 0.5-5 min, the amount of ethylene glycol is 1-3%, and the amount of ozone is 0.2-1.5%; After bleaching, the pulp is not washed, and directly subjected to chlorine dioxide bleaching (D₁), the conditions are as follows: the amount of ClO₂ is 0.2-1.0%, the pulp concentration is 10-15%, pH=2-4, the bleaching temperature is 50-80° C., and the bleaching time is 30-180 min. After bleaching, the pulp is washed and then subjected to E_(OP) stage treatment, the conditions of the E_(OP) stage treatment are as follows: the amount of H₂O₂ is 1-3%, the pulp concentration is 10-15%, pH=11-12, the oxygen pressure is 0.4 MPa, the temperature is 80-90° C., and the alkali treatment time is 30-60 min; After the alkali treatment, the pulp is washed and then bleached with chlorine dioxide bleaching (D₂), the conditions are as follows: the amount of ClO₂ is 0.5-1.0%, the pulp concentration is 10-15%, pH=2-4, the bleaching temperature is 50-80° C., and the bleaching time is 30-180 min. Since there is no washing in the middle, the bleached pulp using X/Z/D₁ or X/D₁/Z process of the present disclosure has better strength performance indexes than bleached pulp using traditional X-Z-D or X-D-Z process.

Further, the specific method of the xylanase-assisted bleaching (X) is as follows: the pulp concentration is adjusted to 10-15%, the pH is adjusted to 5-9, the pulp temperature is maintained at 50-80° C., xylanase is added at a concentration of 5-20 U/g pulp, and stirred evenly for 60-120 min. The study has found that direct ozone and chlorine dioxide bleaching without washing after xylanase treatment is beneficial to the penetration of bleaching agents and the dissolution of lignin, which improves the bleaching efficiency of bleaching agents and improves the bleaching effect of pulp.

Further, the specific method of the ozone bleaching (Z) is as follows: after the pulp is treated with xylanase, the pH value is adjusted to 2.0-4.0, the pulp concentration is maintained at 10-15%, 1-3% ethylene glycol is added, the bleaching temperature is 50-80° C., the mixture is stirred evenly, ozone bleaching is performed, the amount of ozone is 0.3-1.5%, and the bleaching time is 0.5-5 min; utilizing the strong oxidizing and bleaching properties of ozone, the bleaching efficiency and the brightness stability of the pulp are improved, and at the same time, the pollution loading on the environment is reduced.

Further, the specific method of the chlorine dioxide bleaching (D₁) is as follows: after the pulp is bleached by ozone, the pH value is adjusted to 2.0-4.0, the pulp concentration is maintained at 10-15%, the pulp is uniformly mixed at 50-80° C., chlorine dioxide bleaching is carried out, the amount of ClO₂ is 0.2-1.0%, and the bleaching time is 30-180 min; chlorine dioxide is one of the main bleaching agents for pulp bleaching, through the sequential bleaching of X/Z/D₁ or X/D₁/Z stages and the cooperation with subsequent E_(OP) and D₂ bleaching stages, the pulp obtained has high brightness, good strength, and low environmental pollution.

Further, the specific method of the hydrogen peroxide and oxygen reinforced alkali treatment (E_(OP)) is as follows: after the pulp is bleached and washed with chlorine dioxide, the pH value is adjusted to 11-12, the pulp concentration is maintained at 10-15%, 1-3% hydrogen peroxide is added, the oxygen pressure is kept at 0.4 MPa, the temperature is kept at 80-90° C., alkaline hydrogen peroxide bleaching is carried out, and the bleaching time is 30-60 min; by adding hydrogen peroxide and oxygen in the alkali treatment process, it not only improves the brightness of the pulp, but also reduces the amount of chlorine dioxide in the subsequent bleaching process.

Further, the specific method of the chlorine dioxide bleaching (D₂) is as follows: after the pulp is alkali treated and washed, the pH value is adjusted to 2-4, the pulp concentration is maintained at 10-15%, stirred uniformly at 50-80° C., chlorine dioxide bleaching is performed, the amount of ClO₂ is 0.5-1.0%, and the bleaching time is 30-180 min. The residual lignin in the pulp is oxidized by chlorine dioxide bleaching (D₂), and the brightness of the pulp is further improved.

Further, papermaking is performed using the pulp after the bleaching treatment.

Another embodiment of the present disclosure provides a pulp paper-based material prepared by the above method. The paper-based material not only has better physical strength properties, but also has higher brightness.

The present disclosure will be further described in detail below in conjunction with specific embodiments. It should be pointed out that the specific embodiments are for explaining rather than limiting the present disclosure.

In order to enable those skilled in the art to understand the technical schemes of the present disclosure more clearly, the technical schemes of the present disclosure will be described in detail below with reference to specific embodiments.

Brightness measurement: after fluffed by a fiber fluffer, the pulp is made into paper on Kaiser sheet former made in Austria, and then measured by YQ-Z-48B brightness meter;

Folding endurance: it is measured by MIT folding tester made in China;

Bursting index: it is measured by the bursting tester produced by L&W company in Sweden.

Tensile index: it is measured by XLWA(B) intelligent electronic tensile testing machine made in China.

The remaining experimental methods that are not described in detail are conventional experimental methods in this field.

The present disclosure uses xylanase-assisted bleaching, ozone, chlorine dioxide combined with hydrogen peroxide and oxygen reinforced alkali treatment to perform X/Z/D₁-E_(OP)-D₂ bleaching sequence on the pulp to obtain a pulp with low ClO₂ content, high brightness and high strength. The details are as follows:

Comparative Example 1

The steps are as follows:

-   -   (1) The cooking conditions are as follows: the amount of alkali         used was 21%, the liquid ratio was 1:5, the degree of         vulcanization was 25%, the cooking temperature was 170° C., a         small degassing was performed at 105° C., the heating time was         100 min, and the holding time was 90 min; after cooking, the         pulp was washed and screened to prepare an unbleached kraft         pulp.     -   (2) The oxygen delignification conditions are as follows: the         concentration of the unbleached kraft pulp was adjusted to 10%,         the amount of NaOH was 3%, the amount of MgSO₄ was 0.6%, the         oxygen pressure was 0.6 MPa, the temperature was 100° C., the         holding time was 60 min, and then the pulp was washed to prepare         an oxygen delignified pulp.     -   (3) ECF bleaching: The oxygen delignified pulp was bleached by         D-E_(O)-D-D four-stage bleaching. The conditions of D stage         chlorine dioxide bleaching are as follows: the pulp         concentration was 10%, the total amount of ClO₂ in three stages         was 1.5-2.0%, pH=2.0, the bleaching temperature was 60° C., and         the bleaching time was 30-60 min; E_(O) stage was carried out         after washing the pulp, the conditions are as follows: the pulp         concentration was 10-15%, pH=11-12, the oxygen pressure was 0.4         MPa, the temperature was 80-90° C., and the alkali treatment         time was 30-60 min; after bleaching, the pulp was washed.     -   (4) Papermaking: Eucalyptus kraft-cooked natural pulp, oxygen         delignified pulp and D-E_(O)-D-D bleached pulp were respectively         beaten to 35° SR, then fluffed by a fiber fluffer to make it         evenly dispersed, and made into a paper sheet with a basis         weight of 60 g/m² on a paper sheet former.     -   (5) The performance indexes of the obtained eucalyptus         kraft-cooked natural pulp, oxygen delignified pulp and         D-E_(O)-D-D bleached pulp are shown in Table 1.

Table 1 Performance Indexes of Eucalyptus Kraft-Cooked Natural Pulp, Oxygen Delignified Pulp and D-E_(O)-D-D Bleached Pulp

bright- tensile bursting folding ness/ index/ index/kPa · endurance/ Kappa pulp % ISO N · m/g m² · g⁻¹ times number natural pulp 31.2 54.99 5.67 32 13.75 oxygen 61.7 69.23 5.94 35  5.27 delignified pulp D_(0.5)-E_(O)-D_(0.3)-D_(0.2) 86.0 51.71 4.131 47  1.59 bleached pulp D_(0.5)-E_(O)-D_(0.5)-D_(0.5) 87.2 48.47 3.64 29  0.97 bleached pulp D_(0.5)-E_(O)-D_(0.5)-D_(0.5) 88.4 47.49 3.55 24  0.77 bleached pulp

Example 1

The steps are as follows:

-   -   (1) ECF bleaching: the eucalyptus kraft-cooked oxygen         delignified pulp (the specific preparation method is the same as         steps 1) and 2) in Comparative Example 1) was subjected to         X/Z/D-E_(OP)-D or X/D/Z-E_(OP)-D three-stage bleaching.

First, xylanase-assisted bleaching (X) was performed, the conditions are as follows: the amount of xylanase was 10 U/g pulp, the pulp concentration was 15%, pH=5, the bleaching temperature was 55° C., and the bleaching time was 60 min; After the bleaching, the pulp was not washed and directly subjected to ozone bleaching (Z), the bleaching temperature was 55° C., the pulp concentration was 15%, pH=2, the bleaching time was 2 min, the amount of ethylene glycol was 2%, and the amount of ozone was 0.3%; After bleaching, the pulp was not washed, and directly subjected to chlorine dioxide bleaching (D), the process conditions are as follows: the amount of ClO₂ was 0.5%, the pulp concentration was 15%, pH=2, the bleaching temperature was 55° C., and the bleaching time was 30 min; After bleaching, the pulp was washed and then subjected to E_(OP) treatment, the conditions are as follows: the amount of H₂O₂ was 1%, the pulp concentration was 10%, pH=11.5, the oxygen pressure was 0.4 MPa, the temperature was 90° C., and the alkali treatment time was 60 min; After alkali treatment, the pulp was washed and then bleached with chlorine dioxide, the conditions are as follows: the amount of CO₂ was 0.5%, the pulp concentration was 10%, pH=2, the bleaching temperature was 60° C., the bleaching time was 30 min, and the pulp was washed after bleaching. In X/Z/D sequential bleaching, replacing the positions of Z and D does not affect the bleaching result.

-   -   (2) Papermaking: the above bleached pulp was beaten to 35° SP,         then fluffed by a fiber fluffer to make it evenly dispersed, and         made into a paper sheet with a basis weight of 60 g/m² on a         paper sheet former.     -   (3) The performance indexes of the obtained X/Z/D-E_(OP)-D or         X/D/Z-E_(OP)-D bleached pulp are shown in Table 2. The control         group is the oxygen delignified pulp and the pulp prepared after         D-E_(O)-D-D four-stage bleaching sequence. Example 1 is the pulp         prepared after X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.5) three-stage         bleaching sequence.

Table 2 Performance of Eucalyptus X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.5) Bleached Pulp and Control Pulp

bright- tensile bursting folding ness/ index/ index/kPa · endurance/ Kappa pulp % ISO N · m/g m² · g⁻¹ times number natural pulp 31.2 54.99 5.67 32 13.75 oxygen 61.7 69.23 5.94 35  5.27 delignified pulp D_(1.0)-E_(O)-D_(0.5)-D_(0.5) 88.4 47.49 3.55 24  0.77 bleached pulp X₁₀/Z_(0.3)/ 87.8 47.49 4.14 25  1.24 D_(0.5)-E_(OP)-D_(0.5) bleached pulp

As shown in Table 2, the performance of eucalyptus kraft-cooked oxygen delignified pulp after bleaching by X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.5) is as follows: the brightness is 87.8% ISO, the tensile index is 47.49 N·m/g, the bursting index is 4.14 kPa·m²·g⁻¹, the folding endurance is 25 times, and Kappa number is 1.24. Compared with the oxygen delignified pulp in control group, after bleaching by X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.5), the brightness of the pulp is increased by 42.30%, and the Kappa number is decreased by 76.47%. Compared with the D_(1.0)-E_(O)-D_(0.5)-D_(0.5) bleached pulp in control group, when bleached to similar brightness, the amount of chlorine dioxide in X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.5) bleaching sequence is reduced by 50.0%, the tensile index, bursting index and folding endurance have been improved to varying degrees.

Example 2

The steps are as follows:

-   -   (1) ECF bleaching: the eucalyptus kraft-cooked oxygen         delignified pulp (the specific preparation method is the same as         steps 1) and 2) in Comparative Example 1) was subjected to         X/Z/D-E_(OP)-D or X/D/Z-E_(OP)-D three-stage bleaching.

First, xylanase-assisted bleaching (X) was performed, the conditions are as follows: the pulp concentration was 12%, the amount of xylanase was 10 U/g pulp, pH=5, the bleaching temperature was 60° C., and the bleaching time was 60 min; After bleaching, the pulp was not washed and directly subjected to ozone bleaching (Z), the bleaching temperature was 60° C., the pulp concentration was 12%, pH=2, the bleaching time was 3 min, the amount of ozone was 0.3%, and the amount of ethylene glycol was 2%; After bleaching, the pulp was not washed, and directly subjected to chlorine dioxide bleaching (D), the bleaching conditions are as follows: the amount of ClO₂ was 1.0%, the pulp concentration was 12%, pH=2, the bleaching temperature was 60° C., and the bleaching time was 30 min; After bleaching, the pulp was washed and then subjected to E_(OP) stage treatment, the conditions are as follows: the amount of H₂O₂ was 1%, the pulp concentration was 10%, pH=11, the oxygen pressure was 0.4 MPa, the temperature was 90° C., and the alkali treatment time was 60 min; After alkali treatment, the pulp was washed and then bleached with chlorine dioxide, the bleaching conditions are as follows: the amount of ClO₂ was 0.5%, the pulp concentration was 10%, pH=3, the bleaching temperature was 60° C., the bleaching time was 30 min, and the pulp was washed after bleaching. In X/Z/D sequential bleaching, replacing the positions of Z and D does not affect the bleaching result.

-   -   (2) Papermaking: the above bleached pulp was beaten to 35° SR,         then fluffed by a fiber fluffer to make it evenly dispersed, and         made into a paper sheet with a basis weight of 60 g/m² on a         paper sheet former.     -   (3) The performance indexes of the obtained X/Z/D-E_(OP)-D or         X/D/Z-E_(OP)-D bleached pulp are shown in Table 3. The control         group is the oxygen delignified pulp and the pulp prepared after         D-E_(O)-D-D four-stage bleaching sequence. Example 2 is the pulp         prepared after X₁₀/Z_(0.3)/D_(1.0)-E_(OP)-D_(0.5) three-stage         bleaching sequence.

Table 3 Performance of Eucalyptus X₁₀/Z_(0.3)/D_(1.0)-E_(OP)-D_(0.5) Bleached Pulp and Control Pulp

bright- tensile bursting folding ness/ index/ index/kPa · endurance/ Kappa pulp % ISO N · m/g m² · g⁻¹ times number natural pulp 31.2 54.99 5.67 32 13.75 oxygen 61.7 69.23 5.94 35  5.27 delignified pulp D_(1.0)-E_(O)-D_(0.5)-D_(0.5) 88.4 47.49 3.55 24  0.77 bleached pulp X₁₀/Z_(0.3)/ 88.4 47.58 4.07 25  1.20 D_(1.0)-E_(OP)-D_(0.5) bleached pulp

As shown in Table 3, the performance of eucalyptus kraft-cooked oxygen delignified pulp after bleaching by X₁₀/Z_(0.3)/D_(1.0)-E_(OP)-D_(0.5) is as follows: the brightness is 88.4% ISO, the tensile index is 47.58 N·m/g, the bursting index is 4.07 kPa·m²·g⁻¹, the folding endurance is 25 times, and Kappa number is 1.20. Compared with the oxygen delignified pulp in the control group, after bleaching with X₁₀/Z_(0.3)/D_(1.0)-E_(OP)-D_(0.5), the brightness of the pulp is increased by 43.11%, and the Kappa number is decreased by 77.23%. Compared with the D_(1.0)-E_(O)-D_(0.5)-D_(0.5) bleached pulp in control group, when bleached to similar brightness, the amount of chlorine dioxide in X₁₀/Z_(0.3)/D_(1.0)-E_(OP)-D_(0.5) bleaching sequence is reduced by 25.0%, the tensile index, bursting index and folding endurance have been improved to varying degrees.

Example 3

The steps are as follows:

-   -   (1) ECF bleaching: the eucalyptus kraft-cooked oxygen         delignified pulp (the specific preparation method is the same as         steps 1) and 2) in Comparative Example 1) was subjected to         X/Z/D-E_(OP)-D or X/D/Z-E_(OP)-D three-stage bleaching sequence.

First, xylanase-assisted bleaching (X) was performed, the conditions are as follows: the pulp concentration was 11%, the amount of xylanase was 10 U/g pulp, pH=8, the bleaching temperature was 70° C., and the bleaching time was 60 min; After bleaching, the pulp was not washed and directly subjected to ozone bleaching (Z), the bleaching temperature was 70° C., the pulp concentration was 11%, pH=3, the bleaching time was 4 min, the amount of ozone was 0.3%, and the amount of ethylene glycol was 2%; After bleaching, the pulp was not washed, and directly subjected to chlorine dioxide bleaching (D), the process conditions are as follows: the amount of ClO₂ was 0.5%, the pulp concentration was 11%, pH=3, the bleaching temperature was 70° C., and the bleaching time was 30 min; After bleaching, the pulp was washed and then subjected to E_(OP) stage treatment, the process conditions are as follows: the amount of H₂O₂ was 1%, the pulp concentration was 10%, pH=12, the oxygen pressure was 0.4 MPa, the temperature was 80° C., and the alkali treatment time was 60 min; After alkali treatment, the pulp was washed and then bleached with chlorine dioxide, the process conditions are as follows: the amount of ClO₂ was 0.3%, the pulp concentration was 10%, pH=3, the bleaching temperature was 60° C., the bleaching time was 30 min, and the pulp was washed after bleaching. In X/Z/D sequential bleaching, replacing the positions of Z and D does not affect the bleaching result.

-   -   (2) Papermaking: the above bleached pulp was beaten to 35° SR,         then fluffed by a fiber fluffer to make it evenly dispersed, and         made into a paper sheet with a basis weight of 60 g/m² on a         paper sheet former.     -   (3) The performance indexes of the obtained X/Z/D-E_(OP)-D or         X/D/Z-E_(OP)-D bleached pulp are shown in Table 4. The control         group is the oxygen delignified pulp and the pulp prepared after         D-E_(O)-D-D four-stage bleaching sequence. Example 3 is the pulp         prepared after X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3) three-stage         bleaching sequence.

Table 4 Performance of Eucalyptus X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3) Bleached Pulp and Control Pulp

bright- tensile bursting folding ness/ index/ index/kPa · endurance/ Kappa pulp % ISO N · m/g m² · g⁻¹ times number natural pulp 31.2 54.99 5.67 32 13.75 oxygen 61.7 69.23 5.94 35 5.27 delignified pulp D_(0.5)-E_(O)-D_(0.5)-D_(0.5) 87.2 48.47 3.64 29 0.97 bleached pulp X₁₀/Z_(0.3)/ 87.3 51.14 4.17 30 1.24 D_(0.5)-E_(OP)-D_(0.3) bleached pulp

As shown in Table 4, the performance of eucalyptus kraft-cooked oxygen delignified pulp after bleaching by X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3) is as follows: the brightness is 87.3% ISO, the tensile index is 51.14 N·m/g, the bursting index is 4.17 kPa·m²·g⁻¹, the folding endurance is 30 times, and Kappa number is 1.24. Compared with the oxygen delignified pulp in the control group, after bleaching by X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3), the brightness of the pulp is increased by 41.49%, and the Kappa number is decreased by 76.47%. Compared with the D_(0.5)-E_(O)-D_(0.5)-D_(0.5) bleached pulp in control group, when bleached to similar brightness, the amount of chlorine dioxide in X₁₀/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3) bleaching sequence is reduced by 47.13%, the tensile index, bursting index and folding endurance have been improved to varying degrees.

Example 4

The steps are as follows:

-   -   (1) ECF bleaching: the eucalyptus kraft-cooked oxygen         delignified pulp (the specific preparation method is the same as         steps 1) and 2) in Comparative Example 1) was subjected to         X/Z/D-E_(OP)-D or X/D/Z-E_(OP)-D three-stage bleaching sequence.

First, xylanase-assisted bleaching (X) was performed, the conditions are as follows: the pulp concentration was 13%, the amount of xylanase was 15 U/g pulp, pH=8, the bleaching temperature was 80° C., and the bleaching time was 60 min; After bleaching, the pulp was not washed and directly subjected to ozone bleaching (Z), the bleaching temperature was 80° C., the pulp concentration was 13%, pH=3.5, the bleaching time was 1 min, the amount of ozone was 0.3%, and the amount of ethylene glycol was 2%; After bleaching, the pulp was not washed, and directly subjected to chlorine dioxide bleaching (D), the process conditions are as follows: the amount of ClO₂ was 0.5%, the pulp concentration was 13%, pH=3.5, the bleaching temperature was 80° C., and the bleaching time was 30 min; After bleaching, the pulp was washed and then subjected to E_(OP) stage treatment, the process conditions are as follows: the amount of H₂O₂ was 1%, the pulp concentration was 10%, pH=11, the oxygen pressure was 0.4 MPa, the temperature was 90° C., and the alkali treatment time was 60 min; After alkali treatment, the pulp was washed and then bleached with chlorine dioxide, the process conditions are as follows: the amount of ClO₂ was 0.3%, the pulp concentration was 10%, pH=3, the bleaching temperature was 70° C., the bleaching time was 30 min, and the pulp was washed after bleaching. In X/Z/D sequential bleaching, replacing the positions of Z stage and D stage does not affect the bleaching result.

-   -   (2) Papermaking: the above bleached pulp was beaten to 35° SR,         then fluffed by a fiber fluffer to make it evenly dispersed, and         made into a paper sheet with a basis weight of 60 g/m² on a         paper sheet former.     -   (3) The performance indexes of the obtained X/Z/D-E_(OP)-D or         X/D/Z-E_(OP)-D bleached pulp are shown in Table 5. The control         group is the oxygen delignified pulp and the pulp prepared after         D-E_(O)-D-D four-stage bleaching sequence. Example 4 is the pulp         prepared after X₁₅/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3) three-stage         bleaching sequence.

Table 5 Performance of Eucalyptus X₁₅/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3) Bleached Pulp and Control Pulp

bright- tensile bursting folding ness/ index/ index/kPa · endurance/ Kappa pulp % ISO N · m/g m² · g⁻¹ times number natural pulp 31.2 54.99 5.67 32 13.75 oxygen 61.7 69.23 5.94 35  5.27 delignified pulp D_(0.5)-E_(O)-D_(0.5)-D_(0.5) 87.2 48.47 3.64 29  0.97 bleached pulp X₁₅/Z0.3/ 87.5 51.99 4.21 31  1.27 D_(0.5)-E_(OP)-D_(0.3) bleached pulp

As shown in Table 5, the performance of eucalyptus kraft-cooked oxygen delignified pulp after bleaching by X₁₅/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3) is as follows: the brightness is 87.5% ISO, the tensile index is 51.99 N·m/g, the bursting index is 4.21 kPa·m²·g⁻¹, the folding endurance is 31 times, and Kappa number is 1.27. Compared with the oxygen delignified pulp in the control group, after bleaching by X₁₅/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3), the brightness of the pulp is increased by 41.82%, and the Kappa number is decreased by 75.90%. Compared with the D_(0.5)-E_(O)-D_(0.5)-D_(0.5) bleached pulp in control group, when bleached to similar brightness, the amount of chlorine dioxide in X₁₅/Z_(0.3)/D_(0.5)-E_(OP)-D_(0.3) bleaching process is reduced by 47.13%, the tensile index, bursting index and folding endurance have been improved to varying degrees.

Example 5

The steps are as follows:

-   -   (1) ECF bleaching: the eucalyptus kraft-cooked oxygen         delignified pulp (the specific preparation method is the same as         steps 1) and 2) in Comparative Example 1) was subjected to         X/Z/D-E_(OP)-D or X/D/Z-E_(OP)-D three-stage bleaching sequence.

First, xylanase-assisted bleaching (X) was performed, the conditions are as follows: the pulp concentration was 10%, the xylanase dosage was 10 U/g pulp, pH=9, the bleaching temperature was 60° C., and the bleaching time was 60 min; After the bleaching, the pulp was not washed and subjected directly to ozone bleaching (Z), the bleaching temperature was 60° C., the pulp concentration was 10%, pH=2, the bleaching time was 3 min, the amount of ozone was 0.9%, and the amount of ethylene glycol was 2%; After bleaching, the pulp was not washed, and directly subjected to chlorine dioxide bleaching (D), the process conditions are as follows: the pulp concentration was 10%, the amount of ClO₂ was 0.3%, pH=2, the bleaching temperature was 60° C., and the bleaching time was 30 min; After bleaching, the pulp was washed and then subjected to E_(OP) stage treatment, the process conditions are as follows: the amount of H₂O₂ was 1%, the pulp concentration was 10%, pH=11, the oxygen pressure was 0.4 MPa, the temperature was 85° C., and the alkali treatment time was 60 min; After alkali treatment, the pulp was washed and then bleached with chlorine dioxide, the process conditions are as follows: the pulp concentration was 10%, the amount of ClO₂ was 0.2%, pH=2, the bleaching temperature was 60° C., the bleaching time was 30 min, and the pulp was washed after bleaching. In X/Z/D sequential bleaching, replacing the positions of Z and D does not affect the bleaching result.

-   -   (2) Papermaking: the above bleached pulp was beaten to 35° SR,         then fluffed by a fiber fluffer to make it evenly dispersed, and         made into a paper sheet with a basis weight of 60 g/m² on a         paper sheet former.     -   (3) The performance indexes of the obtained X/Z/D-E_(OP)-D or         X/D/Z-E_(OP)-D bleached pulp are shown in Table 6. The control         group is the oxygen delignified pulp and the pulp prepared after         D-E_(O)-D-D four-stage bleaching sequence. Example 5 is the pulp         prepared after X₁₀/Z_(0.3)/D_(0.3)-E_(OP)-D_(0.2) three-stage         bleaching sequence.

Table 6 Performance of Eucalyptus X₁₀/Z_(0.3)/D_(0.3)-E_(OP)-D_(0.2) Bleached Pulp and Control Pulp

bright- tensile bursting folding ness/ index/ index/kPa · endurance/ Kappa pulp % ISO N · m/g m² · g⁻¹ times number natural pulp 31.2 54.99 5.67 32 13.75 oxygen 61.7 69.23 5.94 35  5.27 delignified pulp D_(0.5)-E_(O)-D_(0.5)-D_(0.5) 87.2 48.47 3.64 29  0.97 bleached pulp X₁₀/Z_(0.3)/ 87.2 53.31 4.32 33  1.31 D_(0.3)-E_(OP)-D_(0.2) bleached pulp

As shown in Table 6, the performance of eucalyptus kraft-cooked oxygen delignified pulp after bleaching by X₁₀/Z_(0.3)/D_(0.3)-E_(OP)-D_(0.2) is as follows: the brightness is 87.2% ISO, the tensile index is 53.31 N·m/g, the bursting index is 4.32 kPa·m²·g⁻¹, the folding endurance is 33 times, and Kappa number is 1.31. Compared with the oxygen delignified pulp in the control group, after bleaching by X₁₀/Z_(0.3)/D_(0.3)-E_(OP)-D_(0.2), the brightness of the pulp is increased by 41.33%, and the Kappa number is decreased by 75.14%. Compared with the D_(0.5)-E_(O)-D_(0.5)-D_(0.5) bleached pulp in control group, when bleached to similar brightness, the amount of chlorine dioxide in X₁₀/Z_(0.3)/D_(0.3)-E_(OP)-D_(0.2) bleaching sequence is reduced by 66.67%, the tensile index, bursting index and folding endurance have been improved to varying degrees.

Finally, it should be noted that the above descriptions are only preferred embodiments of the present disclosure and are not intended to limit the present disclosure. Although the present disclosure has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or equivalently replace some of them. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure. Although the foregoing description of the specific implementation of the present disclosure does not limit the scope of protection of the present disclosure, those skilled in the art should understand that on the basis of the technical solution of the present disclosure, those skilled in the art can do it without creative work. The various modifications or variations made are still within the protection scope of the present disclosure. 

1. A short-sequence ECF bleaching process for kraft wood pulp, wherein comprising the following steps: subjecting an oxygen delignified wood pulp to X/Z/D₁ or X/D₁/Z bleaching sequence to prepare a semi-bleached pulp; performing hydrogen peroxide and oxygen reinforced alkaline extraction treatment on the pulp after sequential bleaching; performing a chlorine dioxide supplemental bleaching D₂ on the pulp after the reinforced alkaline extraction treatment to obtain a fully bleached pulp; wherein, in the X/Z/D₁ or X/D₁/Z bleaching sequence, no pulp washing is between X, Z, and D₁ bleaching.
 2. The short-sequence ECF bleaching process for kraft wood pulp according to claim 1, wherein the oxygen delignified wood pulp is made of natural wood pulp by kraft pulping.
 3. The short-sequence ECF bleaching process for kraft wood pulp according to claim 2, wherein the natural wood pulp is prepared by washing and screening wood chips after cooked by kraft pulping, the conditions of cooking are as follows: the amount of alkali used is 21%, the liquid ratio is 1:5, the degree of vulcanization is 25%, the cooking temperature is 170° C., a small degassing is performed at 105° C., the heating time is 100 min, and the holding time is 90 min.
 4. The short-sequence ECF bleaching process for kraft wood pulp according to claim 1, wherein the oxygen delignification is replaced by enhanced oxygen delignification.
 5. The short-sequence ECF bleaching process for kraft wood pulp according to claim 4, wherein the conditions of oxygen delignification are as follows: the concentration of unbleached kraft pulp is adjusted to 10%, the amount of NaOH is 3%, the amount of MgSO₄ is 0.6%, the oxygen pressure is 0.6 MPa, the temperature is 100° C., and the holding time is 60 min.
 6. The short-sequence ECF bleaching process for kraft wood pulp according to claim 1, wherein the conditions of xylanase-assisted bleaching X are as follows: the amount of xylanase is 5-20 U/g pulp, the pulp concentration is 10-15%, pH=5-9, the bleaching temperature is 50-80° C., and the bleaching time is 60-120 min.
 7. The short-sequence ECF bleaching process for kraft wood pulp according to claim 1, wherein the conditions of ozone bleaching Z are as follows: the bleaching temperature is 50-80° C., the pulp concentration is 10-15%, pH=2-4, the bleaching time is 0.5-5 min, the amount of ethylene glycol is 1-3%, and the amount of ozone is 0.2-1.5%.
 8. The short-sequence ECF bleaching process for kraft wood pulp according to claim 1, wherein the conditions for chlorine dioxide bleaching D₁ are as follows: the amount of ClO₂ is 0.2-1.0%, the pulp concentration is 10-15%, pH=2-4, the bleaching temperature is 50-80° C., and the bleaching time is 30-180 min.
 9. The short-sequence ECF bleaching process for kraft wood pulp according to claim 1, wherein the pulp washing is performed between the X/Z/D₁ stage or the X/D₁/Z stage and the E_(OP) stage and the D₂ stage.
 10. The short-sequence ECF bleaching process for kraft wood pulp according to claim 1, wherein the conditions of the E_(OP) stage are as follows: the amount of H₂O₂ is 1-3%, the pulp concentration is 10-15%, pH=11-12, the oxygen pressure is 0.4 MPa, the temperature is 80-90° C., and the alkali treatment time is 30-60 min; or, the conditions of bleaching process in D₂ stage are as follows: the amount of ClO₂ is 0.5-1.0%, the pulp concentration is 10-15%, pH=2-4, the bleaching temperature is 50-80° C., and the bleaching time is 30-180 min.
 11. A fully bleached pulp prepared by the process according to claim
 1. 12. Application of the fully bleached pulp according to claim 11 in the production of paper and cardboard.
 13. The fully bleached pulp according to claim 11, wherein the oxygen delignified wood pulp is made of natural wood pulp by kraft pulping.
 14. The fully bleached pulp according to claim 13, wherein the natural wood pulp is prepared by washing and screening wood chips after cooked by kraft pulping, the conditions of cooking are as follows: the amount of alkali used is 21%, the liquid ratio is 1:5, the degree of vulcanization is 25%, the cooking temperature is 170° C., a small degassing is performed at 105° C., the heating time is 100 min, and the holding time is 90 min.
 15. The fully bleached pulp according to claim 11, wherein the oxygen delignification is replaced by enhanced oxygen delignification.
 16. The fully bleached pulp according to claim 15, wherein the conditions of oxygen delignification are as follows: the concentration of unbleached kraft pulp is adjusted to 10%, the amount of NaOH is 3%, the amount of MgSO₄ is 0.6%, the oxygen pressure is 0.6 MPa, the temperature is 100° C., and the holding time is 60 min.
 17. The fully bleached pulp according to claim 11, wherein the conditions of xylanase-assisted bleaching X are as follows: the amount of xylanase is 5-20 U/g pulp, the pulp concentration is 10-15%, pH=5-9, the bleaching temperature is 50-80° C., and the bleaching time is 60-120 min.
 18. The fully bleached pulp according to claim 11, wherein the conditions of ozone bleaching Z are as follows: the bleaching temperature is 50-80° C., the pulp concentration is 10-15%, pH=2-4, the bleaching time is 0.5-5 min, the amount of ethylene glycol is 1-3%, and the amount of ozone is 0.2-1.5%.
 19. The fully bleached pulp according to claim 11, wherein the conditions for chlorine dioxide bleaching D₁ are as follows: the amount of ClO₂ is 0.2-1.0%, the pulp concentration is 10-15%, pH=2-4, the bleaching temperature is 50-80° C., and the bleaching time is 30-180 min.
 20. The fully bleached pulp according to claim 11, wherein the pulp washing is performed between the X/Z/D₁ stage or the X/D₁/Z stage and the E_(OP) stage and the D₂ stage. 